1. Field
The present invention relates generally to wireless communications, and more specifically to active sets for grant, acknowledgement, and rate control channels.
2. Background
Wireless communication systems are widely deployed to provide various types of communication such as voice and data. A typical wireless data system, or network, provides multiple users access to one or more shared resources. A system may use a variety of multiple access techniques such as Frequency Division Multiplexing (FDM), Time Division Multiplexing (TDM), Code Division Multiplexing (CDM), and others.
Example wireless networks include cellular-based data systems. The following are several such examples: (1) the “TIA/EIA-95-B Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System” (the IS-95 standard), (2) the standard offered by a consortium named “3rd Generation Partnership Project” (3GPP) and embodied in a set of documents including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214 (the W-CDMA standard), (3) the standard offered by a consortium named “3rd Generation Partnership Project 2” (3GPP2) and embodied in “TR-45.5 Physical Layer Standard for cdma2000 Spread Spectrum Systems” (the IS-2000 standard), (4) the high data rate (HDR) system that conforms to the TIA/EIA/IS-856 standard (the IS-856 standard), and (5) Revision C of the IS-2000 standard, including C.S0001.C through C.S0006.C, and related documents (including subsequent Revision D submissions) are referred to as the 1xEV-DV proposal.
In an example system, Revision D of the IS-2000 standard (currently under development), the transmission of mobile stations on the reverse link is controlled by base stations. A base station may decide the maximum rate or Traffic-to-Pilot Ratio (TPR) at which a mobile station is allowed to transmit. Currently proposed are two types of control mechanisms: grant based and rate-control based.
In grant-based control, a mobile station feeds back to a base station information on the mobile station's transmit capability, data buffer size, and Quality of Service (QoS) level, etc. The base station monitors feedback from a plurality of mobile stations and decides which are allowed to transmit and the corresponding maximum rate allowed for each. These decisions are delivered to the mobile stations via grant messages.
In rate-control based control, a base station adjusts a mobile station's rate with limited range (i.e. one rate up, no change, or one rate down). The adjustment command is conveyed to the mobile stations using a simple binary rate control bit or multiple-valued indicator.
Under full buffer conditions, where active mobile stations have large amounts of data, grant based techniques and rate control techniques perform roughly the same. Ignoring overhead issues, the grant method may be better able to control the mobile station in situations with real traffic models. Ignoring overhead issues, the grant method may be better able to control different QoS streams. Two types of rate control may be distinguished, including a dedicated rate control approach, giving every mobile station a single bit, and common rate control, using a single bit per sector. Various hybrids of these two may assign multiple mobile stations to a rate control bit. A common rate control approach may require less overhead. However, it may offer less control over mobile stations when contrasted with a more dedicated control scheme. As the number of mobiles transmitting at any one time decreases, then the common rate control method and the dedicated rate control approach each other.
Grant based techniques can rapidly change the transmission rate of a mobile station. However, a pure grant based technique may suffer from high overhead if there are continual rate changes. Similarly, a pure rate control technique may suffer from slow ramp-up times and equal or higher overheads during the ramp-up times.
Neither approach provides both reduced overhead and large or rapid rate adjustments. An example of an approach to meet this need is disclosed in U.S. patent application Ser. No. 10/780,824, entitled “COMBINING GRANT, ACKNOWLEDGEMENT, AND RATE CONTROL COMMANDS”, filed Feb. 17, 2004, assigned to the assignee of the present invention. In addition, it may be desirable to reduce the number of control channels, while maintaining desirable probability of error for the associated commands on the control channels. There is a need in the art for a system that provides the ability to control the rates of (or the allocation of resources to) both individual mobile stations as well as groups of mobile stations, without unduly increasing channel count. Furthermore, there is a need to be able to tailor the probability of error of various rate control or acknowledgement commands. An example of an approach to meet this need is disclosed in U.S. patent application Ser. No.10/781,285, entitled “EXTENDED ACKNOWLEDGEMENT AND RATE CONTROL CHANNEL”, filed Feb. 17, 2004, assigned to the assignee of the present invention.
While the flexibility of control afforded with combined grant, rate controlled, and acknowledged transmission allows for tailoring of the allocation of system resources, it may be desirable to control the role of various base stations in a system with respect to which signals they transmit and in which allocation controls they may participate. An ad-hoc signaling scheme to provide control may be costly in terms of the overhead required for signaling. Failing to control the reach of some base stations may also cause system performance issues if a grant or rate control command is issued, with effects that are not apparent to the issuing base station. There is therefore a need in the art for efficient management of grant, acknowledgement, and rate control channels.